1. Field of the Invention
The present invention relates to a device for filtering particles from a stream.
2. Brief Description of the Related Art
A sufficient and reliable cooling of components of a flow machine represents an essential aspect for the operation of the flow machine. Modern high temperature gas turbines require a cleverly thought out cooling system to obtain a high efficiency, in particular for cooling the highly loaded turbine blades. The turbine blades therefore have cooling channels, or cavities passing through them and forming cooling channels, through which a cooling medium, particularly cooling air, streams during the operation of the plant. In the leading edge region of the turbine blades, at their forward edge, as a rule numerous cooling air bores are provided, through which the cooling medium can pass outward from the blade interior. A cooling air film forms on the surface in this region, and protects the turbine blade from excessive heating. In the same way, corresponding cooling air bores are also present on the rear edge, the pressure side, and the suction side of the turbine blade and also on other components of the flow machine.
The cooling air is supplied to the cooling channels via one or more supply channels, which for example can be formed by an annular interspace present between the combustion chamber and the external housing of the flow machine. The cooling medium is as a rule a portion of the air compressed by the compressor stage or conducted past this.
A problem in the operation of such a cooling system of a flow machine is represented by the blocking of the cooling channels or cooling air bores by dirt or dust particles which can arise from the atmosphere or from components located upstream of the cooling channels, and brought with the cooling medium into the cooling channels. Blocking of individual cooling channels or cooling air bores can lead to a considerable increase of the local temperature loading of the components to be cooled until they are damaged. This problem is additionally accentuated in that the cooling air bores are increasingly made smaller to increase the efficiency of the cooling system, so that they can more easily become blocked.
For reducing the risk of blockage of cooling channels or cooling bores, it is known to provide additional dust extraction apertures at cooling channel deflections. Particles entrained in the cooling medium are extracted from the cooling medium circuit due to their inertia by means of these dust extraction apertures, so that blockage of the downstream cooling channel bores by these particles is prevented.
An example of an embodiment of a turbine blade with such dust extraction apertures is for example to be gathered from U.S. Pat. No. 4,820,122. The interior of the turbine blade here has cooling channels running in a serpentine manner. The branching into the individual channels already occurs in the region of the entry of the cooling medium into the turbine blade at the rotor. A straight channel extends radially in direct extension of the inlet channel, and leads directly to a dust extraction aperture at the blade tip. The particles entering with the cooling air are forwarded, due to their inertia, directly in a straight line radially of this dust extraction aperture, while nearly dirt-free cooling air can enter without problems into the other, serpentine-like channels. The dirt particles are thus conducted through this dust extraction aperture into free space, so that the cooling air bores cannot be blocked by the dirt particles.
A disadvantage of this technique however consists in that a portion of the cooling medium also emerges through the dirt extraction apertures, so that with this system an undesired loss of cooling medium occurs in the cooling circuit.
It is furthermore known to arrange separators, for example cyclones, within the cooling system to separate the dirt or dust particles from the cooling medium. In these separators, vortices are produced in the cooling medium and the dust and dirt particles, due to their inertia, can be separated off by them from the cooling medium.
A disadvantage of these separators consists in that they require additional constructional space, which is not available in cooling systems for given components to be cooled. Separators are therefore frequently used for applications in which the cooling air is conducted out of the inner region of the flow machine, purified outside the inner region in the separator, and can then be conducted back into the inner region to fulfill the cooling function. Furthermore, cyclones cause a considerable pressure loss and also require an additional cleaning step.
JP 60-205126 describes an apparatus in which an outflow channel with an extension element projects into an inflow channel. The stream cross section of the inflow channel is larger at the place of the opening of the extension element than the stream cross section of the extension. A local acceleration of the stream thereby results, and heavy dust particles, which do not easily follow the stream, enter the outflow channel in a reduced amount. Due to the direct and only slightly curved inflow into the extension element, however, a dust entrainment into the outflow channel which is negligible in all circumstances is not always to be counted on in all circumstances; for example, in the said applications for dust separation in cooling air, according to the place of use of the purified cooling air, one is to go out from an actual null tolerance of dust particles.